Grinding body and manufacturing procedure therefor

ABSTRACT

A grinding foil comprising an abrasive medium on a flexible strip steel foil with a thickness of 0.05 to 0.25 mm and due to the properties of the strip steel foil has good thermal conductivity, thermal stability, tensile strength and selfadhesive properties on a permanently magnetic adhesive backing of a support member allowing fast-release attachment. Due to its ductility, fixing elements are produced in the foil at right angles to its surface and having the shape of inner flanges which engage in matching recesses in the support member, which further improves cooling and enables spot-accurate joining.

BACKGROUND OF THE INVENTION

A thermoplastic foil has become known (German Patent Application byNaxos Union, Frankfurt am Main, published on Oct. 16, 1950, page495-504) and contrary to paper of fabric backings is intended to resistbreaking, as the foil has no pores and the binding agent thereforecannot penetrate the foil. These thermoplastic foils have a thermalstability which is much too low for the intended application. Moreover,the usual abrasive medium backings also have poor thermal conductivity.The mechanical stability is seriously impaired by the poor thermalconductivity and therefore this often leads to premature destruction ofthe abrasive medium backing even before the abrasive coating has beensufficiently utilized. The clamped ends of the abrasive pads or disks oron pad sanders do tear particularly often as they need to be held verytight. There are arranged two expensive clamping means to hold a disk,the ends of which cannot be utilized in grinding. Abrasive disksconstitute a permanent risk of accidents due to their liability tobreak, especially when the frequently interfering guard is removed. Lowtemperature grinding is often only possible by supplying a coolingemulsion.

A further grinding foil is known (U.S. Pat. No. 2,292,991--FLEXIBLEABRASIVE PRODUCT) in which flexible metal foils are proposed as grindingmedium backings, within the thickness range 0.0005 to 0.015 inches, or0.025 to 0.375 mm. In line 33 of page 1, soft steel is named as thegrinding medium backing material. The metal foils consist of soft metalswith a coating of a soft metal serving as a binding means with a lowmelting point and which is caused to melt by the action of heat and isstrewn with the abrasive material, and by means of rolling, part of theabrasive grains is embedded in the metal foil and part into the melt.However, there is no point in this patent document which says anythingabout attaching the grinding foil to a backing material.

Replacing abrasive disks on rotating disk supports by means of aquick-release attachment is enabled by the burr grip, described as earlyas 1959 in the monthly magazine "Popular Mechanics", March edition,volume 8, no. 3, page 28, as a means for securing clothing andupholstery: "Securing by means of nylon strips." Attachment of abrasivedisks was shown for the first time at the Hanover Industrial Fair in1987. One side of the grip is bonded to the abrasive disk, the other oneto the support disk. When the abrasive is used up the paper is disposedof together with the fixing means making the abrasive paper ratherexpensive. Spot-accurate jointing is difficult, static electricity canhardly be leaked off and numerous small interspaces in the burr grip arevery difficult to clean. Another disadvantage is the pressure requiredfor joining. Sterilisation requires easy cleaning, so that applicationin food processing is practically out of question.

Abrasive surfacing or linings are used for peeling on vegetable andgrain peeling machines. In the factory for manufacturing abrasivemedium, an abrasive coating compound consisting of abrasive grains andbinding agent is manually applied at a thickness of approx. 5-25 mm tothe various peeling elements such as peeling plate, peeling drum andpeeling segments, and hardened in an oven. This means that worn peelingelements always must be transported to the factory, which causesconsiderable costs. The necessity of having two peeling machines of thesame design, for instance one for potatoes and one for carrots, is adisadvantage. Potatoes require a more coarse abresive surfacing.Repeated converting of the machine is too expensive.

SUMMARY OF THE INVENTION

The present invention relates to a grinding body with a grinding foilcomprising an abrasive on a flexible abrasive backing and a supportwhich has an adhesive area on its working surface, for firmly holdingthe grinding foil, characterized in, that the abrasive medium backingconsists of a foil of strip steel having thickness of 0.05 to 0.25 mm,the foil of strip steel is provided with fixing elements, the adhesivebacking is permanently magnetic and arranged at right-angles to thesupport surface, in the form of inner flanges of the foil, the supportsurface for accomodating the ring-shaped, tube-like inner flange collarsis provided with matching blind and/or through holes also used assuction holes,

whereby the inner flanges function as cooling elements and as coversbetween grinding foil and adhesive backing, as well as reliablypreventing splinters and grinding dust from penetrating,

and whereby the non-positive or force locked magnetic adhesion of theadhesive backing secures the grinding foil at its place by means of itsmagnetic forces acting at right-angles to the support surface,

so that this magnetic adhesive forces together with the fixing elementslocked in the holes provide for a force locked and a non-positiveengagement between grinding foil and support.

A procedure for manufacturing a grinding body as described above byapplying a fast release grinding foil to a support with an adhesivebacking for securing to the grinding foil, is characterized by the factthat a foil having a thickness of 0.05 to 0.25 mm is coated with anabrasive medium, the foil is equipped with fixing elements in the shapeof inner flanges by extending each of the holes in the foil to produce aring-shaped and tube-like portion, the support is provided with apermanently magnetic adhesive backing and with recesses in line with theinner flanges of the foil, of strip steel, whereby the grinding foil isconnected to the support in such a way that the inner flanges act ascooling elements and at the same time as covers between the grindingfoil and the adhesive backing, and reliably prevent penetration ofsplinters and grinding dust, the force-locked magnetic adhesion of theadhesive backing secures the grinding foil at its place by means of itsmagnetic forces acting at right-angles to the support surface, so thatthis magnetic adhesive forces together with the fixing elements lockedin the holes produce a force-locked non-positive engagement between thegrinding foil and the support.

BRIEF DESCRIPTION OF THE DRAWING

The foregoing will be more readily apparent upon reading the followingdescription in conjunction with the drawing in which the single FIGUREschematically depicts a portion of the grinding body of this invention.

DETAILED DESCRIPTION

A strip steel foil as flexible abrasive medium backing has all of theproperties in order to avoid the disadvantages of conventional abrasivebacking: These being good thermal conductivity, thermal stability andtear resistivity, felxibility and rigidity, plasticity, resistance towater and rotting, electrical conductivity for easy dissipation ofstatic electricity.

Strip steel is known to be produced in very low thickness and it iscommon to denote strips having thicknesses between 0.025 and 0.25 mm asstrip steel foil. Strip steel complying with DIN 1624/1544 was found tobe a low cost and well suited strip steel, and strip steel foils made ofthis material are suitable as abrasive backing at thicknesses from 0.05mm and more. (This is half the thickness of a page of thin typewritingpaper). Strip steel with material number 1.4016 was found to be asuitable non-rusting material, manufactured at thicknesses starting from0.07 mm, which due to its high price can be considered for specialapplications such as a backing for diamond grain.

Permanently magnetic foil is a practical, safe and inexpensive adhesivesupport on the support surface. Anisotropic magnetization gives it thegreatest adhesive power, and at a thickness of 1.5 mm it will meet allof the requirements occurring during the grinding. The specific shapingof the grinding body means according to the invention reduces themagnetic foil thickness to 1 mm while enhancing the shear strength andcooling properties, and also enabling spot-accurate jointing toeliminate imbalance. This is achieved by providing the grinding foil 14having abrasive material 20 with fixing elements arranged atright-angles. The support 10 for the grinding foils have matchingrecesses for these fixing elements. The preferred fixing elements havethe shape of inner flanges 12 obtained by forming the strip steel foil14 (to save material) by extending a hole in such a manner as to obtaina ring-shaped and tube-like part, i.e. the inner flange 12. Thecorresponding recess 16 in the support 10 is a blind or through hole.Two spaced inner flanges 12 result in a punctilious positioning of thegrinding-foil when joining. Shear forces which occur during grinding canbe absorbed depending upon material thickness and number of innerflanges. Those can be calculated as for hollow-type rivets, the shearstrength can have high values even for thin strip steel foils. Theprerequisite of use of magnetic foil 18 at thicknesses specified aboveis that a steel plate 10 approx. 0.2 mm thick is arranged beneath thefoil and on an insulating plate (not shown) of at about 4 mm thickness,in order to obtain sufficient adhesive force. Some grinding machineshave suction holes in the support to suck out debris. In this case theinner flange 12 and hole 16 arrangements in the magnetic foil 18, steelplate base 10 and insulating plate are lined up with the suction holes.This leads to the advantages that the inner flanges 12 reliably preventgrinding dust from penetrating between magnetic foil 18 and grindingfoil 12.

As the shear forces during grinding increase with increasing grain size,the grinding foil strip steel backings are accordingly made thicker andthus having higher tensile strength: 0.05 to 0.25 mm thickness for veryfine, fine medium and coarse grain.

Even without suction in the supports for grinding foils the throughholes, especially in rotating grinding disks, assist is cooling bycausing air turbulence.

Good thermal stability of the strip steel foil makes it expedient to usenot only the usual phenolic and alkyd resins but other binding agentshaving higher thermal stability, too, such as powder coatings of epoxyand polyurethane resins and also organic-anorganic ormosiles, but also aceramic bond such as molten glaze and enamel as used, for example, inthe enamelling industry for continuous coating of strip steel. Here asin the abrasives industry coating is done in an electrostatic field sothat instead of the sticky resin, the melt is coated with grains.

It is presently contemplated that the invention may best be practiced inthe following ways:

1. The simplest way is to cover the strip steel foil with an abrasive ona flexible backing, as the abrsive factory is already equipped with allof the installations required for this.

2. Instead of abresive paper or fabric, strip steel foil is coated inthe electrostatic field using well known procedure for example by meansof alkyd resin as binding agent such as is used for waterproof abrasivepapers.

3. To manufacture grinding foils with particularly high thermalstability, the binding agent powder--for example powder coating,ormosile powder, enamel frit powder--is applied electrostatically andmelted and the grains are strewn electrostatically onto the coating ofmelt.

The grinding foil in the form of an abrasive paper laminate can increasecommercial applicability. This kind of foil can be made self-adhesive,whereby it is less expensive to use thin papers. The flexibility,however, is greater for same foil thickness when the strip steel foil iscoated directly. Grinding foils have a longer service life by being ofconsiderably higher quality. They allow cooler grinding and a quickerreplaceable abrasive surfacing in the form of self-adhesive grindingsurfaces on supports fitted with permanently magnetic foils They allowcool grinding instead of use of grinding disks without guards, andwithout the risks of accidents caused by the breaking disks. They alsoallow secure attachments simply by positioning, even on vibratinggrinders, so no elaborate clamping fixtures are required, and torn beltends belong of the past. Furthermore there is no loss of abrasivematerial by having to clamp the ends of belts. Grinding becomes verycheap in comparison with grinding procedures requiring disks, which isdue to the versatility of the system and the fact that no hardnessgrading is required as it is for grinding disks, making storage easier.Slots can be ground without risk--something which would be verydangerous using a grinding disk with the guard removed. The extremelywide range of applications and the possibility of cool and dry grinding,the easy and fast replacement, the reduced risk of accidents, thepossibility of wet grinding while applying water or underwater grinding,for example for peeling vegetables and grinding stone, the possibilityof having a single peeling machine instead of two, the possibility ofceramic bond for grinding foils, the possibility of total utilization ofgrinding foils by cutting up the used ones to use them on hand sandingblocks until they are fully used up, whereby inner flanges can beproduced by hand, e.g. by punching with a drift punch on a piece of woodand extending the hole with the same drift punch to form the tube-shapedinner flange. For peeling machine drums there is the advantage that theflexible grinding foil automatically lies flat against the wall of thedrum when the wall is lined with magnetic foil. This flexibilitytherefore allows adaptation to any drum radius. In comparison with thethick layer of abrasive on conventional peeling surfaces, the abrasivecoating is much more open and therefore causes more intensive grindingaction. Clogged up peeling surfaces of grinding foils can be removed ina simple step and can even be cleaned by boiling and sterilized which iseven possible with alkyd resin bond. Even under water there is noreduction of adhesive force of the magnetic foil and there is notmaterial fatigue whatsoever as there is in burr grips, which lose asmuch as 50% of their adhesive force.

I claim:
 1. Grinding body with a grinding foil comprising an abrasive ona flexible abrasive backing and a support which has an adhesive area onits working surface, for firmly holding the grinding foil, characterizedin that the abrasive backing consists of a foil of strip steel havingthickness of 0.05 to 0.25 mm, the foil of strip steel is provided withfixing elements, the adhesive backing is permanently magnetic andarranged at right-angles to the support surface, the fixing elements arein the form of ring-shaped, tube-like inner flanges of said foil, andthe support surface for accommodating the ring-shaped, tube-like innerflanges is provided with matching holes also used as suctionholes,whereby the inner flanges function as cooling elements and ascovers between the grinding foil and the adhesive backing, as well asreliably preventing splinters and grinding dust from penetrating betweenthe grinding foil and the adhesive backing, and whereby the magneticadhesion of the adhesive backing secures the grinding foil at its placeby means of its magnetic forces acting at right-angles to the supportsurface, so that the magnetic adhesive forces together with the fixingelements locked in the holes provide for a force locked and anon-positive engagement between the grinding foil and the support. 2.Procedure for manufacturing a grinding body, comprising the stepsof:providing a strip steel foil having a thickness of 0.05 to 0.25 mm;coating said foil with an abrasive medium; equipping said foil withfixing elements in the shape of inner flanges by forming and extendingholes in the foil to produce a ring-shaped and tube-like portion;providing a steel support member having recesses aligned with the innerflanges of the foil; and providing a permanently magnetic adhesivebacking on said support member having recesses aligned with the suppertmember recesses; whereby the grinding foil is connected to the supportmember in such a way that the inner flanges act as cooling elements andat the same time as covers between the grinding foil and the adhesivebacking, and reliably prevent penetration of splinters and grinding dusttherebetween, the force-locked magnetic adhesion of the adhesive backingsecures the grinding foil at its place by means of its magnetic forcesacting at right-angles to the support surface, so that these magneticadhesive forces together with the fixing elements locked in the recessesproduce a force-locked non-positive engagement between the grinding foiland the support member.